Iterator Sample Code

Iterator

Date: 12 Jan 2009

We will use this pattern when we need a routine to loop through a collection of objects, these collections can be anything; an array of pure objects, resultsets from a database, etc. but we'll always need to know if next element exists and be able to retrieve it.
So, we have (See Figure 1):

• An interface that model the behaviour
• A class that will implements this behaviour, and there we can have all the iterators that we want: SQLIterator, FileIterator, AnythingIterator.

All we need to do is call while($iterator->hasNext()) and deal with the next item with $iterator->next()

Sample code

error_reporting(E_ALL);


/**
 * Script to demonstrate the Iterator pattern
 *
 * 12-Jan-2009
 * @author freedelta, http://freedelta.free.fr
 */

/**
 * Iterator - interface.MyIteratorInt.php
 *
 * Interface that models the Iterator behaviour 
 */

interface MyIteratorInt
{

    /**
     * Asks if next element exists
     *
     * @return Boolean
     */

    public function hasNext();


    /**
     * It returns the object itself
     *
     * @return Object
     */

    public function next();
} 


/**
 * Iterator - class.MyIteratorObj.php
 *
 * Class that implements the Iterator interface
 */

class MyIteratorObj implements MyIteratorInt
{
    /**
     * The object to be passed through the constructor parameter
     */

    public $MyObject = null;


    /**
     * A pointer to the current position in the iterator
     */

    public $position = null;

    /**
     * Initializes MyObject and position
     * @param  MyIteratorObj MyObject: any tipe of object
     * @throws Exception
     */

    public function __construct($MyObject)
    {
        if(!isset($MyObject))
        {
            throw new Exception("Collection is empty!");            
        }

        $this->MyObject=$MyObject;

        $this->position=0;

    }

    /**
     * Checks if next item exists
     * @return Boolean
     */
    public function hasNext()
    {   
        // We are on the last item, or array is empty  

        if($this->position >= count($this->MyObject) || $this->MyObject[$this->position]==null)
        {
           return false;
        }
        else
        {
            return true;
        }

     }

    /**
     * This method is invoked only when we know that hasNext()==true
     * @return Object MyIteratorObj
     */

    public function next()
    {
        $item=$this->MyObject[$this->position]; // Get item

        $this->position=$this->position+1;      // Increment position

        return $item;                           // Retrieve item

    }
    
    public function __destruct()
    {    

    }

}



/**
 * Iterator - class.Person.php 
 *
 * Object to test the Iterator pattern
 */
 class Person
 {

    protected $name=null;
 
    public function __construct($name)
    {
        $this->name=$name;  
    }

    public function getName()
    {
        return "My name is: ".$this->name;
    }

 }



// Sample use
  
// Instantiate Persons

$MyObject=array();

$MyObject[0]=new Person("Peter");

$MyObject[1]=new Person("Paul");

$MyObject[2]=new Person("Me");
 

 try
 {
     // Send array of Persons to the Iterator

     $iterator=new MyIteratorObj($MyObject);
  
     while($iterator->hasNext())
     { 
        $currentItem=$iterator->next();

        print " ". $currentItem->getName();

     }

 } 

 catch(Exception $e)
 {
    var_dump($e);
 }


The output will be:
My name is: Peter

My name is: Paul

My name is: Me